In designing programmer/timers for appliances, it is known to provide rotary cams to program making and breaking of a plurality of pairs of electrical contacts at sub-intervals of the interval of rotation of the main program cam drum. In particular, it is also known to provide intermittent rotation of a cam drum by indexing a ratchet wheel connected to the cam with an oscillating drive pawl. The pawl is driven by an intermittent movement mechanism such as a Geneva movement employed to provide rapid advance of the ratchet followed by a dwell.
Heretofore, in mechanisms for providing intermittent rapid advance of the main program cam drum, sub-interval switching has been accomplished by secondary cams which rotate with the Geneva wheel or with an eccentric which oscillates the main drive pawl for driving the ratchet wheel. An example of the former is described in U.S. Pat. No. 4,599,499; and, an example of the latter is described in U.S. Pat. No. 4,577,179. Where the main cam drum indexing ratchet is driven by an intermittent drive mechanism, such as a Geneva mechanism, a sub-interval cam driven by the Geneva mechanism will also be subject to intermittent operation, and thus subject to severe limitation in the range of sub-interval switching which may be provided.